Trainer for enabling the giving of radio instruction



E. L. BAULCH 2,458,550 TRAINER FOR ENABLING THE GIVING OF RADIO INSTRUCTION Filed Dec. 9, '1944 4 Sheets-Sheet 1 Jan. 11,1949.

:g g [MODULA TOR I54 /52 TRANSMITTER CON T/POL 50X AT TOR/VEV 4 Sheets-Sheet 2 INVENTOR By E .LBAULCH ATTORNEY E. L. BAULCH TRAINER FOR ENABLING THE GIVING OF RADIO INSTRUCTION Filed Dec. 9, 1944 Sw monk \ow wow mm; n w I E m QN EQRE US$50 h. 26 Qmw/WM @232 v Jan. 11, 1949.

E. L. BAULCH TRAINER FOR ENABLING THE GIVING OF RADIO INSTRUCTION 4 Sheets-Sheet '4 Filed Dec. 9, 1944 235 ear-- -4 ass 384 I 382 COUPL [N6 v lNl/ENTOR By ELBAULCH AT TORNEV Patented Jan. 11, 1949 UNI TE D sures rnrcm 2,4581550 TRAINERIFOR ENABLING THEGIVINGOE RADIO INSTRUCTION I Erri'estL. Ba'ulchg MillburmNi .L, assignor to Belt Telephone Laboratories,

Incorporated, N 8W2 York; N: Yr, a corporation. -of-New -York- Appiica'tion. December 9, 1944; SerialNo; 567,446

(C1i-35e='14 i 10 Claims invention'relates to-a radio-transmitter and more particularly to the modificatiorr of a transmitter-whereby it may be usedin the training ofairplane crew members in' the proper tunmg" and handling ofa-regular radio transmitter.

There are many instances where radio trans mitting and receiving equipments are very'im-' portant' adjuncts andwhere therefore 'it'is'essential that radiomen betrained' to handle" them efficiently under" all operating" conditions; One such instance; for example; is' on" airplanes.

Modern airplanes; and particularly those'used' inequipment and to b'estcoordinate their endeavors involvingthe used such equipment; it is proposed to provide radio instruction equipment in connection with an airplane crewf'tr'ainer which has been'developed' for givingflighttraining to an" airplane crew. Thisiradio instruction equipment comprises the communication equipment which;

wouldbe installed as'regular equipment on an airplane of the type which the crew trainer is designed to simulate; and a radio instructors desk at which radio receiving, radio transmitting andmonitoring equipment 'is provided to. enable the instructor to transmit such messages and in structions for reception in the trainer" as might be transmitted' fr'om another airplane or from a,

distant'b'ase, for enabling the instructor to receive messages transmitted from transmitters in the trainer, and for enabling the instructor to monitor on'conversations carriedion ov'erth'e interphone system'of the trainer and 'to'monitorr on the operation of'the re'ceivers'an'd tosor'nextent on the transmitters of the trainer.

tion' of A. Ludwig, Serial No. 567,445, filed December'9, 1944.

The present invention is more particularly con cerned with the modification of a transmitter of' the -type ordinarily used-in an airplane for short dista-nce'transmission. 'Since it is not desirable for training purposes to radiate power 'fromth'e transmitter, the transmitter unit is not connected to'2airadiatirig antennabut is shielded and azp'rob'e isu positioned- Within the shield; Whiclfi robe is;

A system ofv thistypeis disclosed in the copending applicao connected by "a coaxial "cable'with the instructors desk Where it" rnayhe connected to a" radio" re ceiver. Since little" power is requiredfdr trans: rriissionover'the short" coaxial cable-tetherinis removee' from the transmitter and a direct current circuitemb'odyingf three" potentiometers, operable from the regular tuning"controls ofthe transmitter;isinsta'lld. rhe-antenn'a reiay unit which fu'nctions'withthe transmitt er"is aisoorriod ified so that the antenna: current indicator 1 of the antenna relay-unit is operable by direct," cur:- rent in simulation ofits-usua1 response ttrthe of the transmitter; 'I'hemastei"osciilatori of the tran'smitter and the resonance indicator of the transmitter are-retained. V

The antenna relay un it is'-modifiedby omitting the antenna" coupling loop-and the'radio'gfre-' quency thermocouple" which" ordinarily wouia cbfitlbl the antenna-current indicator to indicate me antennaload tand m-plac 'thereoflar'iips are" provided" which are connectable in 1 parallel with" tl'ie indic ator" and "in series with the potentiom et'ei' circuits of' thatrans'mitter to provide aj re.-"

si'sttnc temperature coefficient* which" permits the indicator to operate on at similar" resonance curve and to" operate with' approximately the same degree of damping when the indicatoris' deflectedon the output of "athermo'couple:

For operation with 'the"trans1rfitter= the" mode lator unit which would ordinarily;"be"used with the transmitterisemployed 'but'witli the addition of filter' capacitances to reduce the clicks are: received" by," the radio transmitter at the instructors desk" when operating the trans niitter and-by the addition of two relays. one of Which'provides-for the simulatedoperation of the voltage regulator tube" and: modulatoii and" the otherrel'ay' for switchingj resistances into the" tuning= circuit tb;"chan'ge the indication given by? the antenna-current meter with the t operation! of the tone-CW-voice controlof the modulator;

The "jack box" a't the rear of t the transmitter rack been 1 modified" to" include 'a': radio frethe" transmitter to: the cables connected to? the transmitter rack to 'preve'nt'th'e radiation of radio frequer'icyfromsuch leadsi For a clearer understanding of the invention" and "the -n rod of -itsoperation --reference maybehad tb the following detaileddescription when read inconnection with the accompanyin draw ine's in whicrrz Fig; 1A discloses schematically a flight trainer simulating the fuselage of airplane;- night instructors desk, a radio instructors desk, the control bays in which the control apparatus of the trainer is installed, and control and communication cables interconnecting the trainer, the control bays and the instructors desks;

Figs. 1 and 2 taken together show the complete circuit of a radio transmitter modified in accordance with the invention, Fig. 1 showing in the upper portion thereof the modulator unit and in the lower portion thereof the transmitter control box, and Fig. 2 showing in the upper left portion thereof the transmitter rack including the filter circuits, in the lower left portion thereof the antenna relay unit and in the right portion thereof the transmitter unit;

Fig. 3 shows a side elevation view of the transmitter unit, the side of the shielding casing having been cut away;

Fig. 4 is a cross-sectional view of the transmitter unit taken along section line 44 of Fig. 3;

Fig. 5 is a top elevation view with portions broken away to better disclose some of the operating elements of the transmitter; and

Fig. 6 is an isometric view of the potentiometers of the modified transmitter and the gearing by which such potentiometers are controlled from the tuning controls of the transmitter.

The transmitter control box shown in the dotdash rectangle TC in the lower portion of Fig. 1 is installed on the pilots pedestal in the trainer and is provided with a transmitter selector switch I having four selection positions for enablin the selection of any one of four transmitters. When the switch lever is moved to any one of the four indicated selection positions, one of the switches shown immediately below the lever is closed. For example, with the lever positioned as shown to select transmitter N0. 1 the switch IGI is closed as shown. The switch I 02 controls the choice Of emission and has three selection positions indicated as Tone, CW or continuous wave and Voice. When the switch lever is in the No. 1 or Tone position, the switch contacts I03, I04, I and I08 are closed, when the switch lever is in the No. 2 or "CW position switch contacts I03 and I08 are closed and when the switch lever is in the No. 3 or Voice position switch contacts I04, I05, I06, I 01 and I09 are closed as is indicated by the small numerals 1, 2, and 3 appearing adjacent such switch contacts.

The control box is also provided with a poweron switch IIO which controls the connection of direct current to the heater bus bar of the transmitter for supplying operating current to the relays and tube filaments in the circuits of the modulator, transmitter and antenna relay unit of the transmitter. A second switch III is also provided for controlling the connection of a 510- ohm resistance I I2 in series with the microphone circuit to adapt the circuit for the use of a low resistance microphone.

Two jacks are provided into one of which, II3, an outside signaling key SK may be plugged and into the other of which, II4, a microphone may be plugged. If a microphone, such as MIC, equipped with a talk key TX is plugged into jack I I4, then the sleeve of the jack is connected to ground by tightening the knurled nut H5. The nut I I5 is disclosed as in the tightened position which would be used with the microphone MIC. If, however, the microphone MIC, not equipped with a talk key, is plugged into the jack II I, then the nut H5 is loosened and the ground connection to the sleeve of jack H4 is omitted,

4 and to talk, the built-in key H0 or the signaling key plugged into jack I I3 must be used.

The transmitter control box is connected to the modulator shown in the dot-dash rectangle of Fig. 1, labeled Modulator, by a cable terminating at each end in a multiconnection plug, the plug on one end of the cable being insertable into a jack on the control box and the plug on the other end of the cable being insertable into a jack mounted on the modulator casing. For simplicity of illustration this interconnection has been shown schematically as a single plug and jack connection Ill.

The modulator is provided with three tubes, a tone oscillator tube TOS, a modulator tube MOD and a voltage regulator tube VR. For providing plate potential for the tubes of the modulator unit and for the tubes or the transmitter unit the usual dynamotor unit DM is provided which is connected through the coupling plug H8 and coupling jack H9. This unit comprises a direct current motor M which is driven from the 24 to 28-volt source of the trainer connected to the modulator over the plug and jack connection I58 and a direct current generator G capable of generating a direct current potential suitable for the operation of the tubes of the modulator and transmitter. The dynamotor unit is caused to operate whenever the dynamotor relay I20 is operated, the circuit for motor M extending from ground over the No. 1 contacts of plug H8 and jack II9, through the motor armature, thence over the No. 2 contacts of the plug II8 and jack I 59, over contacts of relay I20 and through choke coil I2I to the positive power supply lead I22. The output of the generator G is applied over the No. 3 contacts of plug H8 and jack II9 and through the choke coil I23 to the high potential positive bus bar I 24. The relay I20 is operated when the power-on switch H0 of the control box TC is operated to the on position and when the emission selector switch I02 of the control box is in its No. 1 or No. 2 position for either Tone or CW transmission, over a circuit which may be traced from the battery bus bar I22 over the switch I I0 to the heater bus bar I25 in the modulator, thence through the winding of relay I20 and over switch contacts I00 of the selector switch I 02 to ground. If, however, the switch I02 is in its No. 3 position for Voice emission the circuit traced to the bus bar I25 and through the winding of relay I20 extends over the switch contacts I01 and thence to ground over contacts of the key I I0 or contacts of the key plugged into key jack II3 each time that either one of these keys is operated to talk.

When a key is operated for talking or for either Tone or CW code transmission, a circuit is established upon each closure of the key contacts from battery bus bar I25, through the windings of relays I28 and I2! in parallel and thence to ground applied to the keying conductor I28 over contacts of the operated key. Relay I26 upon operating connects high positive potential from bus bar I 24 through the potential divider comprising resistances I29 and I30 to ground, whereby anode potential is applied from the junction point between these resistances to the anode of tone oscillator tube TOS. Relay I26 also applies potential from bus bar I24 through the potential divider comprising resistances I3I and I32 to ground, whereby anode potential is supplied from the junction point between these resistances through resistance I33 to conductor I34 for supplying anode potential to the anode of the master oscillator tube MOS of the transmitter unit of Fig. 2 as will be later described.

Relay it? upon operating connects the lower section oi the primary winding of transformer Tl over its inner contacts and the contacts "13 of the emission selector switch E82, conductor M5 and contacts of the jack and plug connector I3'B over which the modulator is connected by cable to the receiver rack in the trainer, whereby when the switch 1&2 is set into either the Tone or CW position for code transmission, a side-tone of the transmitted signal may be picked up by the radio receiver of the trainer and heard by the pilot. Relay 82'! also connects the lower right secondary winding of output transformer T3 over its outer contacts and the contacts I06 of switch H32, conductor I35 and thence to thereceiver whereby when the switch M12 is set into its Voice" position a side-tone of the transmitted voice modulated signal may be picked up by the receiver.

Relay i3? is continuously operated when the emission selector switch I02 is set into its No. 3 or Voice position over a circuit extending from battery on bus bar E25, through the winding of relay it? and over the contacts H19 of switch 02 to ground. Relay i31 when operated is effective to establish a shunt over its upper contacts of the oscillator tube 'I'OS to prevent the tube from oscillating should the key H8 or the key plugged into the key jack [l3 be closed to enable talking, if the microphone plugged into jack H4 is not provided with a talk key. In addition, relay l3? removes a shunt from resistance I39 whereby the resistance ground established from conductor 428 upon each operation of a key to talk, to conductor i l!) extending to the transmitter unit is increased for a purpose to be later described.

Relay I 1! is continuously operated when the emission selector switch M32 is set into either its No. 1 Tone or No. 3 Voice position over a circuit extending from battery on the bus bar I25 through the winding of relay l4! and over contacts 184 of switch N32 to ground. Relay l4] when operated, at its lower contacts removes a shunt from resistance M2 whereby the resistance ground applied from conductor I28 upon each operation of the key for tone transmission, to conductor I 40 is further increased for a purpose to be later described. At its upper contacts relay Ml connects the tube VB through resistance I43 across the potential divider including resistances i3! and I32 whereupon tube VE, glows in simulation of the operation of the tube which usually regulates the anode potential applied over conductor 34 to the master oscillator tube MOS of the transmitter unit.

Filament heating current for the tubes TOS and MOD is supplied from battery bus bar I25 serially through such filaments to ground. Anode potential is supplied to the anode of modulator tube MOD from the high potential positive bus bar I24 through the primary winding of output transformer and potential is applied to the screen grid of tube MOD from the junction point between resistances l i l and 145 of the potential divider comprising these resistances, which potential divider is connected between the bus bar we and ground. When the tone oscillator TOS .is operating, that is, on Tone and CW emission, the output of the oscillator tube is-impressed upon the secondary winding of transformer TI and applied to the control grid of the modulator tube MOD. When the emission selector switch 192 is set for Voice emission, at which time the tone oscillator TOS. is not operating, modulating potential is applied to the control grid of modu later tube MOB from the secondary winding of transformer T2 the primary winding of which is connected in a circuit from battery bus bar [25 through resistance F38, through such primary winding, through resistance H2 if the switch MI is open, through the microphone plugged into jack Hid, thence either .over the talk key associated with the microphone. to ground over the sleeve of jack H4 and the ground connection made by the operation of the knurled nut H5, or if the microphone has no. associated talk key, over the ring ofjack I! to ground over the contacts of either key H6 or to ground over the contacts of the key plugged into keying jack H3 when either of such keys is operated to talk.

When the tube MOD is required for modulation, that is, when the emission selector key M12 is in either the Tone or the Voice position, tube MOD is rendered effective by the shunting of the 51,0i10-ohm resistance M6 in the circuit between the cathode of tube MOD and ground. This shunt is established from the junction point between resistances M5 and I4! and over the con tacts 65 of the selector switch 162 to ground. On CW emission or when the master oscillator tube MOS of the transmitter is being operated in accordance with a keyed code, modulation is not required and although the tone oscillator tube TOS also responds in synchronism with the master oscillator tube MOS, its operation is not. effective dueto the blocking resistance I48 which is interposed in the circuit extending through the secondary windings of transformers Ti and T2 and through'the primary winding of transformer T3.

The output of modulator tube MOD is impressed upon the secondary windings of transformer T3 from the lower one of which a side-tone is impressed upon the radio receivers of the trainer as previously described and from the upper one of which a modulated signal potential is impressed upon conductor I34 and thence as presently described upon the anode of the master oscillator tube MOS of the transmitter unit.

The modulator is connected over a cable of conductors with the transmitter rack TR of Fig. 2 upon which two transmitters may be mounted. Each end of the cable is provided with a plug one of which is insertable in a jack in the modulator and the other of which is insertable in a jack on the transmitter rack. For simplification of the disclosure this interconnection has been indicated schematically as a single plug and jack connection I49.

Mounted on the rear of the rack on which two transmitter units are supported is a casing designated TR having five shielded compartments through each of which one of the lead wires incoming from the modulator unit and extending to the transmitter unit passes and terminates in a terminal of .each of two multiterminal plugs. Each of the leads has a filter interposed therein. Such leads are the heater battery lead I25, the anode battery supply and modulated signal input lead 1.34, the direct current tuning lead Hill and two of the transmitter selection leads tell and 15! extending from the transmitter selection switch Hill of the. transmitter control box TC.

These filters each comprise an inductance coil connected in series with the lead, such as the coil 200 connected in series with lead M0, and two condensers, such as 29! and 202, connecting the respeotiue ends of the inductance coil to ground. These filters are provided for the purpose of preventing the radiation of high frequency energy from the leads which interconnect the modulator and the transmitter.

As previously stated, each of these leads termimates in the terminals of two plugs 203 and 234, one allocated to one of the two transmitter units and the other allocated to the other of the two transmitter units. Only one of the transmitter units is disclosed in Fig. 2, being indicated by the apparatus disclosed within the dot-dash rectangle labeled TU. This transmitter unit is assumed to be the No. 1 unit and is connectable to the modulator unit by the insertion of the multiterminal connection plug 203 of the casing TR into the jack 235. The other transmitter is similar to the transmitter TU but would be tuned to a different carrier frequency. This other transmitter would be provided with a jack corresponding to jack 205 into which the plug 204 of the casing TR would be inserted.

The casing TR is provided with an additional plug schematically shown at 236 into which one plug 23? of a cable 208 is inserted and over which cable control leads are extended to the antenna relay unit ARU. For connection with the jack 2H1 of the relay unit the cable 298 is provided with a plug 209.

The antenna relay unit is provided with a relay 2I I, the terminals of the winding of which are connected to the heater battery lead I25 and to the keying lead I28 and is therefore operable each time a key is operated in the transmitter control box TC for talking or for tone or CW code emission to connect battery B connected through resistance 2I2 to the antenna binding post ANT,

over its contacts through the lamp resistances 2 I3, to the transmitter binding post TR and thence by conductor 2I4 to the antenna binding post A of the transmitter unit TU. When the switch 2| 5 is in its right or local position, the antenna current indicator 2I6 is bridged in series with resistance 2I'I across the lamp resistances 2I3. A remotely located antenna current indicator I52 may, if desired, be bridged across the resistances 2I3 when the switch 2 I5 is in its left or remote position over conductors 2I3 and 2I9 extending through the cable 238, over contacts of the plug and jack connections I49 and I I1 and contacts of jack I53 and plug I54.

The transmitter unit TU is equipped with a master oscillator tube MOS and a resonance indicator tube RI. The usual power amplifier equipment has been eliminated from the transmitter since for training purposes only a low output is required. The filaments of the tubes RI and MOS are heated by current conducted over the heater lead I25, over the No. 6 terminals of plug 203, and jack 205, over conductor 220, through resistance 22! and the filament of tube RI in parallel, through the tertiary winding 222 of transformer T4, through the filament of tube MOS and the primary winding 223 of transformer T4 to ground. Current also flows from conductor 220 through the resistances 224 and 225 of a potential divider to ground and potential at the junction point of the potential divider is supplied to the cathode of tube RI.

The cathode of the oscillator tube MOS derives potential from a tap near the upper end of the primary winding of transformer T4 and the grid of this tube is connected through resistance 226, bridged by condenser 22?, to the upper terminal of the primary winding of transformer T4. The lower portion of the primary winding of the transformer is bridged by resistance 228 conrelay 235 when such relay is operated. When the filament of tube MOS is heated and anode potential is thus applied, the tube oscillates at a frequency determined by the tuning imposed by the tuning condensers 23I, 232 and 233. The carrier frequency emitted by the tube may be adjusted to a frequency of 2.1 to 3 megacycles through the adjustment of the condenser 233 by the frequency control knob of the transmitter.

The anodes of the resonance indicator RI are connected by a condenser-resistance network comprising the condenser 236 and resistances 237 and 238 to the anode of tube MOS and the grid of tube RI is connected through resistance 228 and a portion of the primary winding of transformer T4 and through resistance 226 to the grid of tube MOS. The resonance indicator tube RI functions to produce a narrowed shadow condition when the oscillator is tuned to the frequency of the checking crystal 229, A tube of this type is disclosed in Patent No. 2,051,189, granted August 18, 1931, to H. N. Wagner.

The secondary winding of the output transformer T4, which would ordinarily be coupled to the input of a power amplifier stage, is left unconnected and a probe 239 is positioned within the shielded casing of the transmitter which picks up the modulated or unmodulated output of the oscillator tube MOS and transmits it over a coaxial cable 240 to a radio receiver at the instructor's desk as shown schematically in Fig. 1A. On CW transmission, the oscillator tube is caused to start and stop in accordance with a keyed code signal under the control of the keying relay I26 of the modulator and as on this type of emission, no modulation is effective, the tube MOS emits the carrier frequency in accordance with the keyed code signal. On tone modulated emission, the oscillator tube MOS is also caused to start and stop in accordance with a keyed code signal under the control of the keying relay I26, but the tone oscillator tube TOS and modulator tube MOD also function and the anode potential applied to the anode of master oscillator tube MOS is modulated by the 1,009 cycle tone emitted by the oscillator tube TOS. On voice modulated emission, the oscillator tube MOS is caused to start and stop in accordance with the operation of the talk key at the transmitter control box but the tone oscillator tube TOS is prevented from oscillating by ground connected over contact I09 of switch I02 which causes the operation of relay 137, relay I31 upon operating connecting ground over its upper contacts to the grid of tube TOS.

The tuning controls, comprising a frequency control, an antenna inductance control and an antenna coupling control, are retained in the transmitter together with the antenna tuning inductance 24I and the gearing by which it is associated with the antenna tunin control wheel. Two relays 235 and 242 are also provided which are operable in parallel in a circuit from the heating battery lead I25, extending over contacts of 9. plug 2133 and jack .205 to conductor 220, thence through the windings of such relays, over conductor 243, over the No. contacts of jack 205 in plug 293, conductor I59 and over contacts of the plug and jack connection II! to ground over contacts MI of the transmitter selector switch I60 of the transmitter control box, which selector is assumed to be set in position 1 to select the No. 1 transmitter,

Relay 235, upon ope-rating, closes the circuit previously traced over which anode potential and modulated signal potential are applied to the anode of the master oscillator tube MOS and at its inner contacts closes a, direct current tuning circuit which has been added to control the antenna current indicator in simulation of its operation in response to the tuning of the transmitter when power amplifier equipment is used. The direct current tuning circuit may be traced from ground applied to keying conductor I28 in response to the operation of a signaling key or a talk key at the transmitter control box, over the back contacts of relays l3? and MI to conductor I49, or from conductor I28 through resistances 539 and over the back contact of relay I4I to conductor MI] if relay I3! is operated, or from conductor l28 through resistances I39 and M2 to conductor Ml) if relays I31 and MI are both operated, thence over the No. 4 contacts of plug 2!?3 and jack 2%, over the inner contacts of relay 235, through potentiometers PI, P2 and P3, through the antenna tuning inductance 2'4I, over the front contact of relay 252 to antenna terminal A connected by conductor 2M to terminal TR of the antenna relay unit, through the resistance lamps 253 and the front contact of relay 2! I, also operated in response to keying to the terminal ANT. and thence through resistance 2 I2 to battery B and ground.

The antenna current indicator 2I6 being connected through resistance 2! I over the right contacts of switch 2|? and bridging the resistance lamps 2I3, will operate to give an indication of the current flowing over the circuit just traced. This indication will vary in accordance with whether the resistances I39 and I52 are all omitted as when neither relay l 31 or MI is operated on CW emission, with whether the resistance I42 is included as when relay MI is operated on tone emission, with whether the resistances E39 and MI are included as when relay l 31 and IIM are both operated on voice emission, and in accordance with the operation of the potentiometers PI, P2, P3 and the antenna tuning inductance 2A! of the transmitter.

For any one of the three types of signaling emission, indicated in the direct current tuning circuit extending through the antenna relay unit by the inclusion of neither one of the resistances I39 and M2, by the inclusion of resistance H39 and by the inclusion of all resistances H39 and M2; the antenna current indicator 255 will produce a maximum reading when the tuning controls have been operated to positionsin which a regular transmitter would produce its maximum antenna loading for the particular type of signal emission for which the transmitter is being tuned. In a regular transmitter, the antenna current indicator is controlled by a thermocouple which is associated by a coupling loop with the antenna of the transmitter so that the load on the antenna is effective to heat the thermocouple and to thus control the indicator. In the present case since no transmitter antenna emission is present, the direct current tuning circuit simulates such emission, the resistance lamps 2| 3 providing a resistance temperature coefficient which permits the antenna current indicator 2I6 to operate on a resonance curve similar to that upon which it usually operates under thermocouple control and with the same degree of damping.

The manner in which the potentiometers PI, P2 and P3 are controlled by the tuning controls of the transmitter may best be understood by reference to Figs. 3 to 6, inclusive, of the drawing. The transmitter unit has a casing 390 comprising side Walls 30!, 302 and 303, a top wall 304and a removable bottom closure plate 305. The front of the casing is closed by the panel 306 and the casing is divided into a front and a rear compartment by the transverse partition 301, the vertical edges of which are bent to form flanges which are secured to the side walls 30I and 302 by the bolts 308.

Secured to and extending through the rear end of the top wall 394 of the casing are three sockets in which checking crystal 229, the oscillator tube MOS and the resonance indicator tube R-I as disclosed in Fig. 2 are mounted. Two of these sockets are indicated 309 and 3H These tubes and the crystal are enclosed in a removable shield 3I I. This shield is provided with a sight hole (H2, as shown in Fig. 5, directly above the resonance indicator tube through which the tube may be viewed when the frequency output of the transmitter is being adjusted. Mounted on the top wall of the casing adjacent to the tubes is the output transformer T i, disclosed in Fig. 2, which is enclosed in a removable shield 3I3,

Mounted within the casing on the rear wall 303 thereof, is the connection jack 205, inductance coil 234 and relay 242. The antenna binding post A is insulatedly mounted in the front panel 356 and the relay 235 is mounted on the inside of the panel 306.

Mounted within the rear compartment of the casing 308 is the condenser indicated as 233 in Fig. 2, the frame 3M of which is secured by bolts to the underside of the top wall 304 of the casing. To simplify the drawing the plates of the condenser have been indicated by the dotted lines. The shaft 3 I5 of the condenser is journaled in the end members 3H5 and SI! of the frame and has a worm gear 3I8 mounted on the rear end thereof outside the end member 3H5. Secured to the end member 3I6 by screws 3E9 and 329 are two journal blocks 32I and 322 in which the shaft 323 is journaled. Secured to the shaft between the journal blocks and meshed with the gear 3I8 is a driving worm 326 by which the movable plates of the condenser may be adjusted. Secured to the outer faces of the journal blocks 32I and 322 by the screws 3I9 and 32!] is a journal supporting plate 325 to the end of which a third journal block 326 is secured by the screw 32?. Journaled in the block 326 is a shaft 328, the rear end of which is connected to the shaft 323 by the coupling 329 and which shaft has a worm 330 mounted thereon between the journal block 325 and the coupling 329.

The frame 33I of a second condenser, ordinarily used in thev transmitter for tuning the amplifier stage, is mounted within the front compartment of the casing 380 just back of the front panel 306. This frame is secured by bolts to the underside of the top wall 304 of the casing and has one side wall and the condenser plates removed to provide mounting space for gearing "by which the brush of potentiometer PI is driven as will later be described. Secured to the end member 332 of the condenser frame by screws 333, and spaced therefrom by spacers 334 and 335 is the potentiometer P2, the shaft 336 of which extends through the member 332 and has a worm gear 33'. secured to the outer end thereof. Secured to the end member 332 by screws 338 and 339 are two bearing blocks 340 and 34f, the outer ends of which are interconnected by the strap 342 which strap is secured thereto by the screws 338 and 333. J ournaled within the bearing blocks 340 and 34l is a shaft 343 on which is secured the worm 344 meshed with the worm gear 331;

The shaft 343 is aligned with the shafts 328 and 323 and is connected with them through the flexible coupling shaft. The flexible coupling enables the shafts 328 and 323 to be turned by the shaft 343 even though the alignment of the shafts is not exact. Secured to the forward end of shaft 343 and on the outer face of the panel 306, is a knob 346 by which the shafts 343, 345, 328 and 323 and the worms 344, 330 and 324 secured thereto may be turned to rotate the worm gear 331, the worm gear 341 and the worm gear 3I8.

Positioned within the forward compartment of the casing 308 and adjacent and parallel to the removable bottom closure plate 385 is a journal plate 348. This plate is spaced from the wall 304 of the casing 300 by the spacing posts 348, the ends of which are secured to wall 364 and to the journal plate 348 by screws 350. Positioned about the top wall 304 of the casing 366 near the front panel 306 is a journal plate 35f which is spaced from the wall 304 by the journal blocks 352, the ends of which are secured to the wall 304 and to the journal plate 351 by the screws 353.

Journaled in the lower journal plate 348 and in the upper journal plate 35l and extending freely through a hole in the top wall 384 of the casing 300 is a vertical shaft 354 having a worm gear 355 secured thereto near the upper end thereof and having a gear 356 secured at the lower end thereof. Journaled in the journal blocks 352 is a horizontal shaft 351 on which and located between the journal blocks 352 a worm 358 is secured for meshing with the worm gear 355. The shaft 351 carries on the forward end thereof and located outside the panel plate 306, a knob 359 which in the unmodified transmitter is used for controlling the antenna coupling.

Journaled in the lower journal plate 348 and in the top wall 304 of casing 388 is a shaft 360 upon the lower end of which is secured the gear 36l in mesh with the gear 356 as best disclosed in Fig. 6 and, to the upper end of which is secured the slider arm 362 of potentiometer Pl. The winding spool of potentiometer Pl has its mounting flange 363 secured to the gear 364, which gear is freely rotatable with respect to the shaft 360 but is rotatable by the idler gear 365 mounted on the shaft 366. The shaft 368 is also journaled at its lower end in the journal plate 348 and at its upper end in the top wall 34 of the casing 300.

The gear 365 meshes with the gear 361 which is secured to the shaft 368. Shaft 368 is journaled at its lower end in the journal plate 348, extends freely through an opening in the top wall 304 of casing 300 and is journaled at its upper end in the horizontal arm of the bracket 369. The bracket 369 is L-shaped, the vertical arm of which serves to space the horizontal arm from the top wall 304 of the casing and is secured to such top wall by the bolts 316. The forward end of the horizontal arm of the bracket 359 is supported by and secured by screws 31! to the base of a U-shaped bracket 312, the ends of the arms of which are secured by bolts to the upper wall 304 of the casing 300.

Secured to the shaft 368 immediately above the top wall 304 of the casing 300, is a disc 314 to which is secured the mounting flange of the Winding spool of potentiometer P3 whereby the potentiometer winding is rotatable by the shaft 368. The shaft 368 further extends through the sleeve 315 and is rotatable with respect thereto.

" Near its upper end the slider arm 316 of potentiometer P3 is secured. Shaft 368 also has secured thereto a gear 311 which meshes with the gear 318 mounted on the shaft 319.

The shaft 319 is journaled at its lower end in the journal plate 348 and is journaled at its upper end in the journal plate 386 which is secured by screw 38I to the upper surface of the top wall 304 of the casing 300. The shaft 319 also has secured thereto the worm gear 341 previously referred to which is meshed with the worm 330. Thus when the frequency control knob 346 is turned, the worm 330 rotates worm gear 341 and through the gears 318 and 311 rotates the winding of potentiometer P3 and also through the gears 361, 365 and 364 rotates the winding of potentiometer Pl.

Secured to the rear face of the front panel 306 is a U-shaped bracket 382 in the rearwardly extending arms of which is rotatably mounted a drum 383 of insulating material on which is wound the antenna inductance coil 24!. The usual follower slider engages with the coil, being schematically illustrated in Fig. 2. Secured to the shaft on which the drum is mounted is a gear 384 which meshes with a toothed control wheel 385, the wheel 385 being journaled on a stud shaft secured to one arm of the bracket 382 and protruding through a slot in the panel 306 whereby it may be engaged by the fingers of the radio man to rotate the drum 383. In mesh with the gear 384 is a gear 386 secured to the horizontal shaft 381. The shaft 381 is journaled in the vertical arms of the inverted C-shaped bracket 312, the lower inturned ends of the arms of which are secured to the top wall 304 of the casing 300. The shaft has secured thereto the worm 388.

The worm 388 meshes with the worm gear 389 mounted on the vertical shaft 390. Shaft 390 is journaled at its lower end in the top wall 304 of the casing 300 and at its upper end in the horizontal arm of the bracket 369. Also secured to shaft 390 is the gear 39l which meshes with gear 392 secured to the sleeve 315, to which the slider arm 316 of potentiometer P3 is secured. Thus when the control wheel 385 is operated to adjust the antenna inductance 24l by the rotation of the drum 383, the brush of potentiometer P3 is also rotated through the medium of gears 384, 386, 388, 389, 3! and 392.

Secured to the top wall 304 of the casing 300 adjacent to the winding of potentiometer P3 is a lamp socket 393 in which a switchboard lamp 244 is mounted. The winding of each potentiometer PI and P3 has a center tap, as best disclosed in Fig. 2. The terminals of the lamp socket 393 are connected to the center tap and to one end of the winding of potentiometer Pl so that the resistance of lamp 244 is in shunt with one-half 13 of the winding of the potentiometer as disclosed in Fig.2.

The bottom closure plate 305 of the casing 308 has in'sulatedly connected thereto by screws 394 a coaxial thim-ble 395 to which the elbow fitting 396 in which the coaxial cable 240 terminates is secured. The thimble 395 terminates on the inside of the casing 309 in a probe 239, illustrated schematically in Fig. 2, which lies parallel to the closure plate 3%.

The apparatus disclosed in Fig. 3 above the top wall 304 of the casing Sill] is enclosed in a casing 396 illustrated by the dotted lines, this casing having been omitted to better disclose the apparatus. upper casing may be secured to the lower casing in any suitable manner.

Referring to Fig. 2, it will be noted that the sliders of potentiometers Pi and P2 are connected together, that one terminal of the winding of potentiometer P2 is connected to the slider oi potentiometer P3 and that the center tap of the winding of potentiometer P3 is connected to the slider of the antenna tuning inductance coil 24!. The slider of potentiometer P2 being responsive through gears 3'44 and33l to the frequency control knob 3'46, the reading of the antenna current indicator N6 is made to depend upon the choice of transmission frequency selected. Since the winding of potentiometer P3 is also turned by the gears 33?), 341, 318 and 3'7! in response to the operation of the frequency control knob M6, the antenna inductance tuning point is shifted with a variation in frequency and since the winding of potentiometer Pi is also turned by the gears 338, 3E7, 318, 3'11, 381, 365 and 364, in response to the operation or the frequency control knob 3 36, the setting of the antenna loading control is shifted depending upon the frequency selected. The slider of the potentiometer P3 being geared to the antenna inductance control wheel 33 through the gears 334, 38%, 3'88, 389, MI and 392, the slider may be set directly on the center tap of the winding of potentiometer P3 to indicate the resonance point of the antenna indicator. The slider of the potentiometer Pi may be set on the center tap point of the winding of such potentiometer through the gears 358, 355, 3 56 and 36 under the control of the antenna coupling control knob 35s to provide 'a maximum reading of the antenna current indicator '2l6 with a condition of maximum loading.

As these potentiometers are turned so that the sliders 362 and 3% do not rest on center tap points of the windings of potentiometers Pi and P3, the antenna current indicator indicates less than peak current, thus simulating the current readings which result when an actual radio transmitter is tuned to appproach the resonance point or point of maximum antenna coupling. The connection of the lamp resistance 2 in parallel with one-half of the winding of potentiometer 'P-l provides an unsymmetrical decrease in the antenna current when the antenna 'cou-' pling control is turned to move the slider of potentiometer P! to the right or left of the center tap position.

While the invention has been described in connection with a transmitter particularly adapt-ed for use in training equipment for training the 1 operating crew of an airplane, it will be obvious that the invention is equally applicable to other training purposes.

The transmitter is, as disclosed. schematically in Fig. 1A, connected with a radio instructors desk over a coaxial cable 240 so that the instructor is able to determine from a radio receiver which he has tuned to receive on the allocated wavelength if the crew man in the trainer has correctly set the transmitter to transmit on the proper Wavelength and with the propertype of emission. The equipment at the instructors desk is fully disclosed in the Ludwig application hereinbefore referred to. The transmitter of the present invention also enables the crew man to operate the transmitter to secure a response of the antenna current indicator to indicate the proper antenna load for the typ of emission selected.

What is claimed is:

1. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for controlling said frequency in accordance with signals which it is desired to transmit, tuning controls, an antenna current indicator, a source of current, and potentiometers operable by said controls for deriving a potential from said source and for applying it. to said indicator whereby said indicator is operated in simulation of its usual operation in accordance with antenna loading in response to the actual tuning of the amplifier equipment of a regular radio transmitter.

2. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for controlling said frequency in accordance with keyed code signals,

means for modulating said frequency in accordance with keyed code signals, means for modulating said frequency in accordance with voice signals, means for selecting the type of emission to be used, tuning controls, an antenna current indicator, a source of current, means for deriving a potential from said source which Varies in accordance with which of the frequency control or modulation means is selected for use, and potentiom'eters operable by said tuning controls for modifying said derived potential and for applying said modified potential to said indicator whereby said indicator is operated in simulation of its usual operation in accordance with the antenna loading for the selected type of emission in response to the actual tuning of the amplifier equipment of a regular radio transmitter.

6. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for selectively determining whether said frequency shall be controlled in accordance with keyed code signals, shall bemodulated in accordance with keyed code signals or shall be modulated in accordance with voice signals, tuning controls, an antenna current indicator, a source of direct current, means controlled by said frequency control selector for deriving a potential from said source which varies in accordance with the type of frequency control selected, and po'tentiometers operable by said tuning controls for modifying said derived potential and for applying said modified potential to said indicator whereby said indicator is operated in simulation of its usual operation in accordance with the antenna loading for the selected type of emission in response to the actual tuning of the amplifier equipment of a regular radio transmitter.

4. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for selectively determining whether said frequency shall be controlled in accordance with keyed code signals, shall be modulated in accordance with keyed code signals, or shall be modulated in accordance with voice signals, tuning controls, an antenna current indicator, a source of direct current, a series of resistances, means controlled by said frequency control selector for selectively associating said resistances with said source of current for deriving a potential from said source which varies in accordance with the type of frequency control selected, and potentiometers operable by said tuning controls for modifying said derived potential and for applying said modified potential to said indicator whereby said indicator is operated in simulation of its usual operation in accordance with the antenna loading for the selected type of emission in response to the control of the tuning of the amplifier equipment of a regular radio transmitter.

5. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for controlling said frequency in accordance with signals which it is desired to transmit, tuning controls, a source of current, a lamp resistance, an antenna current indicator in bridge of said resistance, and potentiometers operable by said tuning controls for deriving a potential from said source and for impressing it upon said resistance, whereby said indicator is operated on a similar resonance curve and with approximately the same degree of damping as it would in operating in accordance with antenna loading in response to the actual tuning of the amplifier equipment of a regular radio transmitter.

6. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for controlling said frequency in accordance with signals which it is desired to transmit, tuning controls, a coaxial system, a probe for picking up said carrier frequency and for applying it to said coaxial system, an antenna current indicator, a source of current, and potentiometers operable by said tuning controls for deriving a potential from said source and for applying it to said indicator, whereby said indicator is operated in simulation of its usual operation in accordance with antenna loading in response to the actual tuning of the amplifier equipment of a regular transmitter.

7. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for controlling said frequency in accordance with signals which it is desired to transmit, a control for determining the frequency to be generated, a control for varying the inductance of the antenna circuit, a control for varying the antenna coupling, an antenna current indicator, a source of current, and potentiometers operable by said controls for deriving a potential from said source and for applying it to said indicator whereby said indicator is operated in simulation of its usual operation in accordance with the antenna loading in response to the actual tuning of the amplifier equipment of a regular radio transmitter by said controls.

In a device for simulating the operation of a radio transmitter, an oscillator, for generating a carrier frequency, means for controlling said frequency in accordance with signals which it is desired to transmit, a control for determining the frequency to be generated, a control for varying the inductance of the antenna circuit, a control for varying the antenna coupling, an antenna current indicator, a source of current, a first potentiometer the winding of which is rotatable by said frequency control and whose slider is operable by said antenna coupling control, a second potentiometer whose slider is operable by said frequency control, and a third potentiometer whose winding is rotatable by said frequency control and whose slider is operable by said antenna inductance control, said potentiometers being jointly effective to derive a potential from said source and to apply it to said indicator whereby said indicator is operated in simulation of its usual operation in accordance with the antenna loading in response to the actual tuning of the amplifier equipment of a regular radio transmitter by said controls.

9. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for controlling said frequency in accordance with signals which it is desired to transmit, a control for determining the frequency to be generated, a control for varying the inductance of the antenna circuit, a control for varying the antenna coupling, an antenna current indicator, a source of current, a first potentiometer whose center-tapped winding is rotatable by said frequency control and Whose slider is operable by said antenna coupling control, a second potentiometer whose slider is electrically connected to the slider of said first potentiometer and is rotatable by said frequency control, and a third potentiometer whose centertapped winding is rotatable by said frequency control and whose slider is electrically connected with one terminal of the winding of said second potentiometer and is operable by said antenna inductance control, said potentiometers being jointly effective to derive a potential from said source and to apply it to said indicator whereby said indicator is caused to produce a maximum deflection for the frequency selected when the sliders of said first and third potentiometers are at the center tap positions of their windings in simulation of the usual operation of said indicator in accordance with the antenna loading in response to the actual tuning of the amplifier equipment of a regular radio transmitter by said controls.

10. In a device for simulating the operation of a radio transmitter, an oscillator for generating a carrier frequency, means for controlling said frequency in accordance with signals which it is desired to transmit, a control for determining the frequency to be generated, a control for Varying the inductance of the antenna circuit. a control for varying the antenna coupling, an antenna current indicator, a source of current, a first potentiometer whose center-tapped winding is rotatable by said frequency control and whose slider is operable by said antenna coupling control, a second potentiometer whose slider is electrically connected with the slider of said first potentiometer and is operable by said frequency control, a third potentiometer whose center-tapped winding is rotatable by said frequency control and whose slider is electrically connected with one terminal of the winding of said second potentiometer and is operable by said antenna inductance control, and a lamp resistance in shunt of one half of the winding of said first potentiometer whereby said potentiometer produces an unsymmetrical response when its slider is positioned on opposite sides of the center-tap position of said winding, said potentiometers being jointly effective to derive a potential from said source and to apply it to said indicator whereby said indicator is caused to produce a maximum deflection for ance with the antenna loading in response to the 5 actual tuning of the amplifier equipment of a regular radio transmitter by said controls.

ERNEST L. BAULCI-I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,119,083 Link May 31, 1938 2,312,962 De Florez Mar. 2, 1943 2,352,216 Melvin June 27, 1944 

